Processes for making methacrylic acid

ABSTRACT

Processes are described for making methacrylic acid via methacrolein from a biobased isobutene, wherein the biobased isobutene is prepared from ethanol or from acetic acid in the presence of a Zn x Zr y O z  mixed oxide catalyst, the biobased isobutene is oxidized to methacrolein and the methacrolein is further oxidized to methacrylic acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application from U.S. patentapplication Ser. No. 14/683,257, filed Apr. 10, 2015, which was acontinuation of International Application No. PCT/US2013/067036 filedOct. 28, 2013, now published as WO 2015/005942, which directly claimsthe benefit of U.S. Provisional Application Ser. No. 61/844,998, filedJul. 11, 2013; the U.S. patent application Ser. No. 14/683,257 was alsoa continuation of International Application No. PCT/US2013/063968 filedOct. 9, 2013, now published as WO 2014/092849, which directly claims thebenefit of U.S. Provisional Application Ser. No. 61/737,312 filed Dec.14, 2012; and, the U.S. patent application Ser. No. 14/683,257 was alsoa continuation of International Application No. PCT/US2013/062784 filedOct. 1, 2013, now published as WO 2014/070354, which directly claims thebenefit of U.S. Provisional Application Ser. No. 61/720,433 filed Oct.31, 2012.

TECHNICAL FIELD OF THE INVENTION

The present application concerns processes for making methacrylic acidvia methacrolein from isobutene.

BACKGROUND ART

In this regard, isobutene is widely used for the production of a varietyof industrially important products, and has been used to makemethacrylic acid via methacrolein in one commercially known route.Isobutene has however been produced commercially to date through thecatalytic or steam cracking of fossil feedstocks. As fossil resourcesare depleted and/or become more costly to use, renewable source-basedroutes to isobutene are increasingly needed—especially in considerationof increased demand for isobutene.

A hard-template method has previously been described for synthesizingZn_(x)Zr_(y)O_(z) mixed oxides for the direct and high yield conversionof ethanol (from the fermentation of carbohydrates from renewable sourcematerials, including biomass) to isobutene, wherein ZnO was added toZrO₂ to selectively passivate zirconia's strong Lewis acidic sites andweaken Brönsted acidic sites while simultaneously introducing basicity.The objectives of the hard template method were to suppress ethanoldehydration and acetone polymerization, while enabling a surface basicsite-catalyzed ethanol dehydrogenation to acetaldehyde, an acetaldehydeto acetone conversion via aldol-condensation/dehydrogenation, and aBrönsted and Lewis acidic/basic site-catalyzed acetone-to-isobutenereaction pathway.

High isobutene yields were in fact realized, but unfortunately, as laterexperienced by Mizuno et al. (Mizuno et al., “One-path and SelectiveConversion of Ethanol to Propene on Scandium-modified Indium OxideCatalysts”, Chem. Lett., vol. 41, pp. 892-894 (2012)) in their effortsto produce propylene from ethanol, it was found that furtherimprovements in the catalyst's stability were needed.

SUMMARY OF THE INVENTION

Our U.S. Patent Application Ser. No. 61/720,433 (the “'433application”), filed Oct. 31, 2012 for “Stable Mixed Oxide Catalysts forDirect Conversion of Ethanol to Isobutene and Process for Making”,concerned the discovery that these improvements could be realizedwithout adding modifying metals and without a reduction in the initialhigh activity (100 percent ethanol conversion) that had been observed inthese mixed oxide catalysts. The '433 application thus in sum concernedan improved stability, longer lifetime catalyst for converting ethanolto isobutene.

Separately, we discovered that acetic acid, rather than ethanol, may beconverted to a biobased isobutene product using certain mixed oxidecatalysts, including a mixed oxide catalyst as made in the '433application. This discovery became the basis for U.S. Patent ApplicationSer. No. 61/737,312 (the “'312 application”), filed Dec. 14, 2012 for“Process and Catalyst for Conversion of Acetic Acid to Isobutene”.

Building on these discoveries, the present invention in one aspectconcerns a process for making methacrylic acid via methacrolein from abiobased isobutene, wherein the biobased isobutene is prepared fromethanol in the presence of a Zn_(x)Zr_(y)O_(z) mixed oxide catalyst, thebiobased isobutene is oxidized to methacrolein and the methacrolein isoxidized to methacrylic acid.

In certain embodiments according to this first aspect, theZn_(x)Zr_(y)O_(z) mixed oxide catalyst exhibits improved stability forthe conversion, exhibiting less than 10 percent loss, more preferablyless than 5 percent loss and still more preferably less than 2 percentloss in isobutene selectivity over a period of 200 hours on stream. Inother embodiments, the Zn_(x)Zr_(y)O_(z) mixed oxide catalyst is made bya process as described in the '433 application, broadly comprisingforming a solution of one or more Zn compounds, combining one or morezirconium-containing solids with the solution of one or more Zncompounds, drying the wetted solids, then calcining the dried solids.

In a second, related aspect, the present invention concerns a processfor making methacrylic acid via methacrolein from a biobased isobutene,wherein the biobased isobutene is prepared from acetic acid in thepresence of a catalyst, the biobased isobutene is oxidized tomethacrolein and the methacrolein is oxidized to methacrylic acid. Incertain embodiments, the catalyst is a Zn_(x)Zr_(y)O_(z) mixed oxidecatalyst, especially a catalyst made by a process as described in the'433 application, and the process of making the starting biobasedisobutene is carried out as described in the '312 application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a process for producing a wholly biobasedmethacrylic acid from a wholly biobased isobutene made from ethanol inthe presence of a Zn_(x)Zr_(y)O_(z) mixed oxide catalyst, especiallysuch a catalyst made by a process as described in the '433 application.

FIG. 2 schematically depicts a process for producing a biobasedmethacrylic acid, particularly a wholly biobased methacrylic acid, froma biobased and especially a wholly biobased isobutene made from aceticacid, according to the second aspect of the present invention assummarized above.

DESCRIPTION OF EMBODIMENTS

Referring now to FIG. 1, a process 10 is schematically illustratedwherein ethanol 12 is converted to isobutene 14 in the presence of acatalyst, particularly, a Zn_(x)Zr_(y)O_(z) mixed oxide catalyst. Theisobutene 14 is then combined with oxygen from an oxygen source 16 andoxidized to yield methacrolein, which is then oxidized with oxygen fromoxygen source 16 to provide a methacrylic acid product 18.

The ethanol 12 is conventionally derived from biological carbon sources,for example, by fermentation of five- and especially six-carbon sugars,so that the isobutene 14 and subsequent methacrylic acid product 18 aredesirably wholly-biobased.

Parenthetically, by “biobased”, we mean those materials whose carboncontent is shown by ASTM D6866 to be derived from or based insignificant part (at least 20 percent or more) upon biological productsor renewable agricultural materials (including but not being limited toplant, animal and marine materials) or forestry materials. “Whollybiobased” thus will be understood as referring to materials whose carboncontent by ASTM D6866 is entirely or substantially entirely (forexample, 95 percent or more) indicated as of biological origin.

In this respect ASTM Method D6866, similar to radiocarbon dating,compares how much of a decaying carbon isotope remains in a sample tohow much would be in the same sample if it were made of entirelyrecently grown materials. The percentage is called the biobased contentof the product. Samples are combusted in a quartz sample tube and thegaseous combustion products are transferred to a borosilicate break sealtube. In one method, liquid scintillation is used to count the relativeamounts of carbon isotopes in the carbon dioxide in the gaseouscombustion products. In a second method, 13C/12C and 14C/12C isotoperatios are counted (14C) and measured (13C/12C) using accelerator massspectrometry. Zero percent 14C indicates the entire lack of 14C atoms ina material, thus indicating a fossil (for example, petroleum based)carbon source. One hundred percent 14C, after correction for thepost-1950 bomb injection of 14C into the atmosphere, indicates a moderncarbon source. ASTM D6866 effectively distinguishes between biobasedmaterials and petroleum derived materials in part because isotopicfractionation due to physiological processes, such as, for example,carbon dioxide transport within plants during photosynthesis, leads tospecific isotopic ratios in natural or biobased compounds. By contrast,the 13C/12C carbon isotopic ratio of petroleum and petroleum derivedproducts is different from the isotopic ratios in natural or bioderivedcompounds due to different chemical processes and isotopic fractionationduring the generation of petroleum. In addition, radioactive decay ofthe unstable 14C carbon radioisotope leads to different isotope ratiosin biobased products compared to petroleum products.

The ethanol 12 can in this regard be derived from any known processwhereby five and/or six carbon sugars from conventional grain millingoperations or from processing of a lignocellulosic biomass moregenerally may be converted to one or more products inclusive of ethanol,at least in some part by fermentation means. Both aerobic and anaerobicprocesses are thus contemplated, using any of the variety of yeasts(e.g., kluyveromyces lactis, kluyveromyces lipolytica, saccharomycescerevisiae, s. uvarum, s. monacensis, s. pastorianus, s. bayanus, s.ellipsoidues, candida shehata, c. melibiosica, c. intermedia) or any ofthe variety of bacteria (e.g., clostridium sporogenes, c. indolis, c.sphenoides, c. sordelli, candida bracarensis, candida dubliniensis,zymomonas mobilis, z. pomaceas) that have ethanol-producing capabilityfrom five and/or six carbon sugars under aerobic or anaerobic conditionsand other appropriate conditions. The particular yeasts (or bacteria)used and other particulars of the fermentations employing these variousyeasts (or bacteria) are a matter for routine selection by those skilledin the fermentation art.

However obtained, the ethanol 12 is then according to a first aspect ofthe invention converted to isobutene 14 in the presence preferably of aZn_(x)Zr_(y)O_(z) mixed oxide catalyst as described in the '433application, having excellent stability for the conversion of ethanol toisobutene in exhibiting less than 10 percent loss in isobuteneselectivity over a period of 200 hours on stream under atmosphericpressure (<5 psig) and at 450° C., at full conversion of the ethanol 12to the isobutene 14. Preferably, however, the catalyst exhibits lessthan 5 percent loss in isobutene selectivity over a period of 200 hourson stream, and more preferably less than 2 percent.

These Zn_(x)Zr_(y)O_(z) mixed oxide catalysts are generallycharacterized by a Zn/Zr ratio (x:y) of from 1:100 to 10:1, preferablyfrom 1:30 to 1:1, especially 1:20 to 1:5, and still more preferably 1:12to 1:10.

Parenthetically, in the present application where any range of values isgiven for any aspect or feature of the mixed oxide catalysts or anyprocess described for using the mixed oxide catalysts, the given rangeswill be understood as disclosing and describing all subranges of valuesincluded within the broader range. Thus, for example, the range of 1:100to 10:1 will be understood as disclosing and describing not only thespecific preferred and more preferred subranges given above, but alsoevery other subrange including a value for x between 1 and 10 and everyother subrange including a value for y between 1 and 100.

The catalysts made by the method of the '433 application are consistentin their particle size with catalysts made by the hard template methoddescribed in Sun et al., “Direct Conversion of Bio-ethanol to Isobuteneon Nanosized Zn_(x)Zr_(y)O_(z) Mixed Oxides with Balanced Acid-BaseSites”, Journal of the American Chemical Society, vol. 133, pp11096-11099 (2011), wherein carbon black (BP 2000 carbon black fromCabot Corp.) was used as a hard template for the synthesis of nanosizedZn_(x)Zr_(y)O_(z) mixed oxides. In the hard template method ofmanufacture described in Sun, the BP 2000 template was dried at 180° C.overnight. Calculated amounts of zirconyl nitrate hydrate(Sigma-Aldrich, greater than 99.8% purity) and Zn(NO₃)₂.6H₂O(Sigma-Aldrich, greater than 99.8% purity) were dissolved in a givenamount of water, and sonicated for 15 minutes to produce a clearsolution with desired concentrations of Zn and Zr. About 25 grams of theobtained solution were then mixed with 6.0 grams of the preheated BP2000 to achieve incipient wetness, and the mixture was transferred to aceramic crucible and calcined at 400 degrees Celsius for 4 hours,followed by ramping the temperature to 550 degrees Celsius (at a ramprate of 3 degrees Celsius/minute) and holding at 550 degrees Celsius foranother 20 hours. Nanosized white powders were obtained, having a meanparticle size of less than 10 nanometers. The catalysts made by themethod of the '433 application and used in the method of FIG. 1 (forconverting ethanol 12 to isobutene 14) likewise comprise aggregates ofless than 10 nm-sized particles, with a highly crystalline structure.The Zn oxide component is again highly dispersed on the Zr oxidecomponent.

As summarized in the '433 application, some characteristic differenceshave, however, also been observed between catalysts of equivalent Zn/Zrratios made by the prior hard template method and by the method of the'433 application. For example, average crystallite size as calculatedbased on the Scherer equation will typically be larger, for example, 8.4nanometers for a Zn₁Zr₁₀O₂ mixed oxide catalyst prepared according tothe '433 application as compared to 4.8 nanometers for a Zn₁Zr₁₀O₂ mixedoxide catalyst prepared according to the former hard template method.

A Zn₁Zr₁₀O₂ mixed oxide catalyst prepared according to the method of the'433 application also has a smaller surface area, roughly 49 squaremeters per gram, as compared to 138 square meters per gram for aZn₁Zr₁₀O₂ mixed oxide catalyst prepared according to the former hardtemplate method.

One further, compositional difference was also observed betweencatalysts prepared by the two methods, in that the Zn_(x)Zr_(y)O_(z)mixed oxide catalysts according to the '433 application preferably aresubstantially sulfur-free, containing less than 0.14 weight percent ofsulfur, as compared to, for example, 3.68 weight percent of sulfur inthe same Zn₁Zr₁₀O₂ mixed oxide catalyst prepared according to the formerhard template method.

The Zn_(x)Zr_(y)O_(z) mixed oxide catalysts of the '433 application andpreferred for use herein have improved stability for the conversion ofethanol 12 to isobutene 14; while the contributions if any of the largercrystallite size and smaller surface area to this improved stability arenot presently understood, it is nevertheless believed that at least themuch reduced sulfur content of the inventive catalysts does contributematerially to this improved stability.

Based on infrared analyses of catalysts prepared according to the '433application and according to the hard template method (which analysesare described more fully in the incorporated '433 application), thepresence of sulfur in the former catalysts—presumably left behind fromthe Cabot BP 2000 furnace black hard template after the template's beingsubstantially removed by a controlled combustion—appeared to havecontributed to the presence of a number of stronger Lewis and Brönstedacidic sites on catalysts made by the former method and in turn to agreater degree of acidic site-catalyzed coking of catalysts madeaccording to the former hard template method.

Accordingly, while from one perspective the Zn_(x)Zr_(y)O_(z) mixedoxide catalysts preferred for use in the present invention can becharacterized in practice as having improved stability for theconversion of ethanol to isobutene, exhibiting less than 10 percent lossin isobutene selectivity over a period of 200 hours on stream, from adifferent, compositional perspective the preferred more stableZn_(x)Zr_(y)O_(z) mixed oxide catalysts can be characterized ascontaining less than 0.14 percent by weight of sulfur. Preferably, stillmore stable catalysts are provided, having a sulfur content of less than0.01 percent by weight, and still more preferably the catalysts willhave a sulfur content of less than 0.001 percent by weight.

Such catalysts may be made by a process broadly comprising, in certainembodiments, forming a solution of one or more Zn compounds, combiningone or more zirconium-containing solids with the solution of one or moreZn compounds so that the solution wets the zirconium-containing solidsto a state of incipient wetness, drying the wetted solids, thencalcining the dried solids. In other embodiments, a solution is formedof one or more Zr compounds, the solution is combined with one or moreZn-containing solids so that the solution wets the Zn-containing solidsto a state of incipient wetness, the wetted solids are dried and thenthe dried solids are calcined. In principle, provided the zinc andzirconium compounds and solids in these embodiments do not containsulfur, any combination of zinc and zirconium materials and any solventcan be used that will permit the zinc and zirconium components to mixhomogeneously whereby, through incipient wetness impregnation, one ofthe zinc or zirconium components are well dispersed on a solid of theother component for subsequent drying and conversion to the oxide formsthrough calcining.

The conditions and times for the drying and calcining steps will depend,of course, on the particular zinc and zirconium materials and solventused, but in general terms, the drying step can be accomplished in atemperature range of from 60 degrees Celsius to 200 degrees Celsius overat least about 3 hours, while the calcining can take place at atemperature of from 300 degrees Celsius to 1500 degrees Celsius, butmore preferably a temperature of from 400 to 600 degrees Celsius isused. The calcination time can be from 10 minutes to 48 hours, with from2 to 10 hours being preferred.

In still other embodiments, suitable Zn_(x)Zr_(y)O_(z) mixed oxidecatalysts can also be prepared by a hard template method, except that asuitable very low sulfur content carbon is used for the hard templatesuch that the finished catalyst will contain not more than 2 percent byweight of sulfur, especially not more than 0.5 percent by weight ofsulfur and still more preferably will contain not more than 0.1 weightpercent (by total weight of the catalyst) of sulfur. A variety of suchvery low sulfur carbons are available commercially from varioussuppliers; in general, the lower the sulfur content, the better forforming the highly active, stable mixed oxide catalysts preferred foruse in a process of the present invention (whether based on ethanol asin FIG. 1 or acetic acid as in FIG. 2).

Processes for converting the ethanol 12 to isobutene 14 using thesecatalysts may be conducted in a manner and under conditions described inthe Sun journal article, or in a manner and under conditions describedin Mizuno et al or the several other prior publications concerned withthe production of products inclusive of isobutene from ethanol. In thisregard, while Mizuno et al. is particularly directed to the productionof propylene from ethanol, it is nevertheless considered to be wellwithin the capabilities of those skilled in the art to determine whatconditions embraced by Mizuno et al. or other similar references will bemost appropriate to produce isobutene among the possible products,without undue experimentation. Accordingly, a detailed description ofprocess details for using the more stable mixed oxide catalysts need notbe undertaken herein. Nevertheless, as an example, a continuous fixedbed reactor or flow bed reactor can be used. The reaction temperaturemay be in a range from 350 to 700 degrees Celsius, preferably, in arange from 400 to 500 degrees Celsius, and the WHSV can be in a rangefrom 0.01 hr⁻¹ to 10 hr⁻¹, preferably from 0.05 hr⁻¹ to 2 hr⁻¹.Ethanol/water solution with steam to carbon ratios from 0 to 20,preferably from 2 to 5 can be used.

Once the isobutene 14 is formed, the isobutene 14 is oxidized withoxygen from an oxygen source 16 to yield methacrolein according to anyknown process and using any known catalyst for this purpose, and themethacrolein is further oxidized to produce a methacrylic acid product18, again according to any known process and using any known catalystfor the second oxidation step from methacrolein to methacrylic acid.

A number of patents have been issued describing methods for producingmethacrylic acid from isobutene via a methacrolein intermediate, thoughthose skilled in the art will be aware that the following are given asmerely non-limiting examples of the various processes and catalysts thathave been and continue to be described in the patent and generalscientific literature relating to a part of such a process or theprocess as a whole.

U.S. Pat. No. 8,273,313 to Galloway describes a system and process forseparating methacrolein from methacrylic acid and acetic acid in the gasphase product from a partial oxidation of isobutene in two oxidationsteps, purportedly maximizing recovery of all three components atminimum capital and energy cost, under conditions minimizingpolymerization and plugging by solids deposition in compressors, columnsand the like. A number of patents and publications are recited fordisclosing aspects of a process of partially oxidizing isobutene or anisobutene equivalent into methacrylic acid in a single step ormulti-step oxidation process, for example, U.S. Pat. No. 4,544,054; U.S.Pat. No. 4,618,709; U.S. Pat. No. 4,925,981; U.S. Pat. No. 4,956,493;U.S. Pat. No. 4,987,252; U.S. Pat. No. 5,356,460; U.S. Pat. No.5,780,679 and WO 0345083.

U.S. Pat. No. 7,732,367 to Stevenson et al. concerns a catalyst foraccomplishing the gas-phase methacrolein oxidation to methacrylic acidand methods of making the catalyst, where the catalyst includes at leastmolybdenum, phosphorus, vanadium, bismuth and a first component selectedfrom potassium, rubidium, cesium, thallium or mixtures or combinationsof these, has at least 57% medium pores and a nitric acid to molybdenumratio of at least 0.5 to 1 or a nitric acid to Mo₁₂ ratio of at least6.0:1.

U.S. Pat. No. 5,231,226 to Hammon et al. also relates particularly tothe gas-phase oxidation of methacrolein to methacrylic acid, disclosinga process for the catalytic gas-phase oxidation of methacrolein tomethacrylic acid in a fixed-bed reactor at elevated temperature oncatalytically-active oxides with a single pass conversion of from 45 to95 percent. Because of the exothermicity of the reaction, the reactiontemperature is maintained from 280 to 340 degrees Celsius until amethacrolein conversion of from 20 to 40 percent is reached, at whichpoint the reaction temperature is reduced at once, incrementally orcontinuously by from 5 to 40 degrees Celsius until a conversion of from45 to 95 percent has been accomplished, with the proviso that thereaction temperature is not less than 260 degrees Celsius. Suitablecatalysts are indicated as those described in EP 265733, EP 102688 andDE 3010434.

U.S. Pat. No. 5,155,262 to Etzkorn et al. concerns both processes forthe oxidation of isobutene to methacrolein and for the oxidation ofisobutene to methacrylic acid in two stages with methacrolein as anintermediate, wherein prior methods using steam in the starting reactantgas mixture to avoid flammable gas mixtures and to improve reactionselectivity are assertedly improved by using essentially inert,essentially anhydrous diluent gases in place of the steam. Reducedwastewater load, improved selectivity and reduced byproduct formationare said to result from the substitution. Etzkorn et al. recite that“many oxidation catalysts have been disclosed for producing methacroleinin high yield by oxidizing isobutene”, col. 1, lines 60-62, giving asexamples catalysts containing mixed oxides of molybdenum, bismuth andiron with phosphorus or tungsten or antimony, and commonly incorporatingcobalt and/or nickel and alkali metals as promoters, col. 1, lines62-65. For the second stage oxidation of methacrolein to methacrylicacid, mixed metal oxide catalysts are described which are said totypically contain molybdenum, vanadium, tungsten, chromium, copper,niobium, tantalum and antimony. Etzkorn et al. refer in this regard to anumber of additional publications predating those listed in U.S. Pat.No. 8,273,313, including U.S. Pat. No. 4,147,885; U.S. Pat. No.3,475,488; U.S. Pat. No. 3,171,859; U.S. Pat. No. 4,267,386 and U.S.Pat. No. 4,267,385, as well as UK 2,068,947 and U.S. Pat. No. 4,618,709.

Turning now to FIG. 2, a process is schematically illustrated accordingto a second aspect of the present invention, providing biobased andpreferably wholly biobased methacrylic acid via methacrolein from acorresponding biobased and preferably wholly biobased isobutene, whereinthe isobutene is prepared from acetic acid in the presence of acatalyst, the biobased isobutene is oxidized to methacrolein and themethacrolein is oxidized to methacrylic acid. In certain embodiments,the catalyst is a Zn_(x)Zr_(y)O_(z) mixed oxide catalyst, especially acatalyst made by a process as described in the '433 application, and theprocess of making the starting biobased isobutene is carried out asdescribed in the incorporated '312 application.

More particularly, a process 20 is shown wherein acetic acid 22 isconverted to isobutene 24, and the isobutene 24 is oxidized (asdescribed above in connection with FIG. 1) using oxygen from an oxygensource 26 to provide a methacrylic acid product 28. As further describedin the '312 application and as is well appreciated by those skilled inthe art, the acetic acid 22 can be obtained by various methods from anumber of starting materials. If desired, at least a portion of theacetic acid that is conventionally produced in the oxidation ofisobutene 24 through methacrolein to the methacrylic acid product 28 canbe recovered and recycled to form a portion of the acetic acid 22 thatis used.

For example, the acetic acid 22 can be produced from a source 30 of fiveand six carbon sugars by fermentation. U.S. Pat. No. 6,509,180 and U.S.Pat. No. 8,252,567 seek to improve upon known processes for makingethanol and butanol/hexanol, respectively, by means including thefermentation of five and six carbon sugars into acetic acid. In U.S.Pat. No. 6,509,180, the acetic acid is esterified to form an acetateester which may then be hydrogenated (using hydrogen from, e.g., steamreforming of natural gas, electrolysis of water, gasification of biomassor partial oxidation of hydrocarbons generally) to ethanol. In U.S. Pat.No. 8,252,567, the ethanol formed in this manner can be used to makebutanol and hexanol, by subjecting the ethanol with acetate, acetic acidor mixtures thereof to an acidogenic fermentation using, for example,species of the bacteria Clostridium (Clostridium kluyveri is mentioned),to produce butyrate, butyric acid, caproate, caproic acid or mixturesthereof. These materials then in turn are acidified to convert butyrateand caproate to butyric acid and caproic acid, the butyric and caproicacids are esterified and then the butyric and caproic acid estersundergo reduction by hydrogenation, hydrogenolysis or reduction bycarbon monoxide to provide butanol and ethanol.

As related in these two patents and as is well known to those skilled inthe fermentation art, the fermentation of the five and six carbon sugars30 to form acetic acid 22 can be accomplished by various organisms. Moreparticularly, homoacetogenic microorganisms are able throughfermentation to produce acetic acid with 100% carbon yield; thesemicroorganisms internally convert carbon dioxide to acetate, in contrastto a process for producing ethanol from sugars obtained from biomass,wherein carbon dioxide is produced as a byproduct.

Examples of homoacetogens given by U.S. Pat. No. 8,252,567 aremicroorganisms of the genus Moorella and Clostridium, especiallymicroorganisms of the species Moorella thermoaceticum (described asformerly classified as Clostridium thermoaceticum) or Clostridiumformicoaceticum. U.S. Pat. No. 8,252,567 represents that about onehundred known acetogens in twenty-two genera were known as of 2009, andcross-references Drake, et al., Ann. N.Y. Acad. Sci. 1125: 100-128(2008) for a review of acetogenic microorganisms.

Other references describing fermentation methods for producing aceticacid from five and six carbon sugars include U.S. Pat. No. 4,935,360;U.S. Pat. No. 8,236,534; U.S. Pat. No. 4,513,084; U.S. Pat. No.4,371,619 and U.S. Pat. No. 4,506,012; both one-step fermentationprocesses from the sugars to acetic acid, acetates or both aredisclosed, as well as two-step processes involving a first fermentationto lactic acid (by lactobacillus or known methods of homolacticfermentation, preferably) followed by a second fermentation to convertlactic acid to acetic acid, for example, using Clostridiumformicoaceticum.

Any of the known fermentation methods may, in short, be used asdescribed in the '312 application to produce acetic acid 22 forconversion to isobutene 24 in the presence of the Zn_(x)Zr_(y)O_(z)mixed oxide catalysts, but homoacetogenic fermentation methods areconsidered preferable in that carbon dioxide is not produced as abyproduct—the carbon dioxide represents a yield loss from the overallprocess to make isobutene and as a greenhouse gas is undesirableparticularly in the context of a process to make a needed product moresustainably from renewable resources.

As well or in the alternative, the acetic acid feedstock 22 can be madefrom ethanol 32, according to any of several known methods employingoxidative fermentation with acetic acid bacteria of the genusAcetobacter.

As well or in the alternative, the acetic acid feedstock 22 can be madefrom methanol 34 through combination with carbon monoxide according tothe most industrially used route for making acetic acid, for example, inthe presence of a catalyst under conditions effective for thecarbonylation of methanol. A variety of carbonylation catalysts areknown in this regard, see, for example, U.S. Pat. No. 5,672,743; U.S.Pat. No. 5,728,871; U.S. Pat. No. 5,773,642; U.S. Pat. No. 5,883,289;U.S. Pat. No. 5,883,295.

In regard to the production of methanol 34, with increasing concerns forthe abatement of greenhouse gases such as carbon dioxide in recentyears, a substantial amount of work has been reported on methods toconvert carbon dioxide to methanol, see, for example, Wesselbaum et al.,“Hydrogenation of Carbon Dioxide to Methanol by Using a HomogeneousRuthenium-Phosphine Catalyst”, Angew. Chem. Int. Ed., vol. 51, pp7499-7502 (2012); Ma et al., “A Short Review of Catalysis for CO₂Conversion”, Catalysis Today, vol. 148, pp 221-231 (2009); Borodko etal., “Catalytic Hydrogenation of Carbon Oxides—a 10-Year Perspective”,Applied Catalysis A: General, vol. 186, pp 355-362 (1999); and U.S. Pat.No. 8,212,088 to Olah et al., “Efficient and Selective ChemicalRecycling of Carbon Dioxide to Methanol, Dimethyl Ether and DerivedProducts” and the various additional references cited in each of these.Those skilled in the art will thus be well-acquainted with processes andassociated catalysts for producing methanol 34 from carbon dioxide (suchas may be produced in the production of ethanol 32 by fermentation orrecovered from combustion processes or other industrial emissions) andfrom carbon dioxide, carbon monoxide and hydrogen derived from thegasification of a biomass, though it will be appreciated that methanol34 or these “building block” gases can alternately or additionally beobtained from a biomass by anaerobic digestion through methane, fromelectrolysis of water using energy from geothermal sources, byelectrolytic cleavage of carbon dioxide to produce carbon monoxide andwater and so forth. As well, it will be appreciated that the methanol 34could be prepared from methane from natural gas, but preferably asubstantial proportion and more preferably all of the methanol 34 usedwill be wholly biobased.

The production of the more stable mixed oxide catalysts of the '433application and the use of mixed oxide catalysts to convert both ofethanol and acetic acid to isobutene are demonstrated for purposes ofillustration in the following non-limiting examples:

Example 1

Commercial zirconium hydroxide was dried at 120 degrees Celsius for morethan 5 hours. Calculated amounts of Zn(NO₃)₂ (from Sigma-Aldrich, morethan 99.8 percent purity) were dissolved in water to form a series ofclear solutions. Dried zirconium hydroxide (also from Sigma-Aldrich,more than 99.8 percent purity) was then mixed with the solutions in turnby incipient wetness, in order to form wet powders impregnated with Znin certain proportions to the zirconium in the form of the driedzirconium hydroxide powder. The wetted powders were then dried at 80degrees Celsius for 4 hours, followed by calcination at 400 degreesCelsius for 2 hours and at 600 degrees Celsius for 3 hours to obtain aseries of Zn_(x)Zr_(y)O_(z) catalysts.

Ethanol to isobutene runs were conducted with the catalysts thusprepared in a fixed-bed stainless steel reactor, having an insidediameter of 5 millimeters. A given amount of catalyst was packed betweenquartz wool beds. A thermocouple was placed in the middle of thecatalyst bed to monitor the reaction temperatures. Before beginning thereaction, the catalyst beds were first pretreated by flowing 50ml/minute of nitrogen at 450 degrees Celsius through the catalyst over ahalf hour, then a mixture of ethanol/water at steam to carbon ratiosfrom 1 to 5 was introduced into an evaporator at 180 degrees Celsius bymeans of a syringe pump and carried into the reactor by the flowingnitrogen carrier gas. Meanwhile, the product line was heated to inexcess of 150 degrees Celsius before a cold trap, to avoid condensingthe liquid products in the product line.

A Shimadzu 2400 gas chromatograph equipped with an auto sampling valve,HP-Plot Q column (30 m, 0.53 mm, 40 μm) and flame ionization detectorwas connected to the line between the reactor outlet and cold trap tocollect and analyze the products in the effluent gas. After the coldtrap, an online micro-GC (MicroGC 3000A equipped with molecular sieves5A, plot U columns and thermal conductivity detectors) was used toanalyze the product gases specifically, using nitrogen as a referencegas.

An ethanol/water solution (steam to carbon ratio of 2.5) was thensupplied by flowing N₂ to the reactor at a weight hourly space velocity(WHSV) of 0.95 hr⁻¹. The ethanol concentration was 15.1 percent byweight, and the reaction temperature was 450 degrees Celsius. Ethanolconversion was 100% throughout, and isobutene selectivity declined byless than 2 percent over 200 hours on stream for the series of catalystsprepared as described.

Thermogravimetric and differential scanning calorimetry analysis of therecovered, spent catalysts showed only about 0.7 weight percent of cokeafter 207 hours onstream.

Example 2

Commercial zirconium hydroxide was dried at 120 degrees Celsius for morethan 5 hours. A calculated amount of Zn(NO₃)₂ (from Sigma-Aldrich, morethan 99.8 percent purity) was dissolved in water, forming a clearsolution. The dried zirconium hydroxide (which was also fromSigma-Aldrich, more than 99.8 percent purity) was then mixed with thesolution by incipient wetness, in order to form wet powders impregnatedwith Zn. The wetted powder was then dried at 80 degrees Celsius for 4hours, followed by calcination at 550 degrees Celsius for 3 hours, toobtain a Zn₁Zr₈O_(z) catalyst.

An acetic acid to isobutene process was conducted with the catalyst thusprepared in a fixed-bed stainless steel reactor having an insidediameter of 5 millimeters. 100 mg of the catalyst was packed betweenquartz wool beds. A thermocouple was placed in the middle of thecatalyst bed to monitor the reaction temperature. Before beginning thereaction, the catalyst bed was pretreated by flowing 50 ml/minute ofnitrogen at 450 degrees Celsius through the catalyst over a half hour. A25 weight percent solution of acetic acid in water was then introducedinto an evaporator at 180 degrees Celsius by means of a syringe pump,and the vaporized steam/acetic acid was carried into the reactor by aflowing nitrogen carrier gas at an acetic acid concentration in the gasphase of 1.36 weight percent and a WHSV of 0.1 grams of acetic acid pergram of catalyst per hour. Meanwhile, the product line was heated to inexcess of 150 degrees Celsius before a cold trap, to avoid condensingthe liquid products in the product line. A reaction temperature of 415degrees Celsius was employed.

A Shimadzu 2400 gas chromatograph equipped with an auto sampling valve,HP-Plot Q column (30 m, 0.53 mm, 40 μm) and flame ionization detectorwas connected to the line between the reactor outlet and cold trap tocollect and analyze the products in the effluent gas. After the coldtrap, an online micro-GC (MicroGC 3000A equipped with molecular sieves5A, plot U columns and thermal conductivity detectors) was used toanalyze the product gases specifically, using nitrogen as a referencegas.

A consistent product of about 5 percent by weight of methane, about 10percent by weight of acetone, about 33 percent by weight of carbondioxide and more than about 50 percent by weight of the desiredisobutene product was obtained; in contrast to the ethanol to isobuteneprocess using these same Zn_(x)Zr_(y)O_(z) mixed oxide catalysts inExample 1, no ethylene or propylene was produced. The catalyst showedvery high stability over the full duration of the run, with no signs ofobservable deactivation after more than 1400 minutes of time-on-streamoperation.

Examples 3 Through 31

A number of additional catalysts were prepared by first dryingcommercial zirconium hydroxide at 120 degrees Celsius for more than 5hours. Calculated amounts of Zn(NO₃)₂ (from Sigma-Aldrich, more than99.8 percent purity) were dissolved in water to form a series of clearsolutions. The dried zirconium hydroxide (also from Sigma-Aldrich, morethan 99.8 percent purity) was then mixed with the solutions in turn byincipient wetness, in order to form wet powders impregnated with Zn incertain proportions to the zirconium in the form of the dried zirconiumhydroxide powder. The wetted powders were then dried at 80 degreesCelsius for 4 hours, followed by calcination at the temperatureindicated in Table 1 below for 3 hours, to obtain a series ofZn_(x)Zr_(y)O_(z) catalysts by an incipient wetness method. Thesecatalysts were used to convert ethanol to isobutene in the manner ofExample 1. Particular reaction conditions, whether the reactiontemperature, WHSV or steam to carbon ratio, for example, were varied tocompare the effect on the selectivities to acetone and isobutene at fullconversion of the ethanol. For several of the catalysts, some amount ofsulfur was purposely doped into the catalyst to assess the effect ofsulfur at those certain levels on the selectivities to acetone and toisobutene. Thus, the catalyst for example 28 was doped with 10 ppm ofsulfur, while for example 29 the catalyst was doped with 50 ppm ofsulfur and for example 30 with 200 ppm (by weight).

TABLE 1 Additional Ethanol to Isobutene Runs Calcination Reaction WHSVSteam to Acetone Isobutene Zn/Zr temp temp (g_(ethanol)/ carbon Ethanolselectivity selectivity Ex # ratios (° C.) (° C.) g_(catal)/hr) ratio(gas wt %) (mol %) (mol %) 3  1/6.5 550 450 0.19 5 1.0 3.5 46.4 4  1/6.5550 425 0.08 5 1.0 4.0 49.8 5 1/8  550 450 0.19 5 1.0 3.4 47.3 6 1/8 550 415 0.08 5 1.0 8.5 51.4 7 1/10 550 450 0.19 5 1.0 2.9 49.2 8 1/10550 425 0.08 5 1.0 3.8 51.5 9 1/12 550 450 0.19 5 1.0 2.5 48.9 10 1/12550 450 0.08 5 1.0 0.5 45.5 11 1/12 550 425 0.08 5 1.0 3.8 51.6 12 1/12550 415 0.08 5 1.0 6.2 51.3 13 1/14 550 450 0.19 5 1.0 4.9 46.8 14 1/10500 450 0.19 5 1.0 0.7 47.6 15 1/10 500 475 0.19 5 1.0 0 41.9 16 1/10500 450 0.08 5 1.0 0 42.7 17 1/10 500 425 0.08 5 1.0 1.2 49.3 18 1/10600 475 0.19 5 1.0 7.2 42.3 19 1/10 600 450 0.19 5 1.0 13.7 42.1 20 1/10600 450 0.08 5 1.0 4.3 43.8 21 1/10 600 425 0.08 5 1.0 12.9 44.8 22 1/10600 400 0.08 5 1.0 32.6 33.1 23 1/10 650 450 0.19 5 1.0 32.2 30.1 241/10 650 450 0.08 5 1.0 10.6 41.8 25 1/10 650 425 0.19 5 1.0 44.9 23.026 1/10 650 425 0.08 5 1.0 26.1 37.4 27 1/10 650 415 0.08 5 1.0 34.132.3 28 1/10 550 415 0.08 5 1.0 7.3 52.1 29 1/10 550 415 0.08 5 1.0 6.352.4 30 1/10 550 415 0.08 5 1.0 8.4 51.2 31 1/8  550 450 0.31 2.5 15.02.8 53.5

Examples 32 Through 40

For these additional examples of converting acetic acid to isobutene,additional Zn_(x)Zr_(y)O_(z) mixed oxide catalysts were prepared both bythe incipient wetness method (IW in Table 2 below) but also by the priorart hard template method (HT), and these were evaluated and the productsanalyzed using the same apparatus and method described above but underdifferent sets of reaction conditions (as summarized in Table 2 below).

TABLE 2 Further Acetic acid to Isobutene Examples Reaction WHSV Steam toAcetone Isobutene Zn/Zr temp. (g_(acetic)/ carbon C_(G-acetic acid)selectivity selectivity Ex # Catalyst ratio (° C.) g_(catal)/hr) ratio(wt %) (mol %) (mol %) 32 HT 1/15 450 0.25 5 1.3 30.5 41.7 33 HT 1/15450 1.14 5 1.5 61.1 18.4 34 IW 1/8  415 0.1 5 1.4 9.8 52.5 35 IW 1/10415 0.95 5 22.3 50.8 20.1 36 IW 1/10 450 0.16 2.5 18.8 0.7 50.6 37 IW1/10 450 0.65 2.5 18.8 8.3 46.9 38 IW 1/10 415 0.16 2.5 18.8 5.7 57.2 39IW 1/10 415 0.33 2.5 18.8 16.4 45.3 40 IW 1/10 415 0.65 2.5 18.8 30.535.0

The invention claimed is:
 1. A process for making methacrylic acid viamethacrolein from a biobased isobutene, comprising: in a single, firststep and without isolating any intermediate species, converting aceticacid to isobutene in the presence of a mixed oxide catalyst comprised ofoxides of Zn and Zr in which the ratio of Zn:Zr is from about 1:100 toabout 10:1; oxidizing the isobutene to methacrolein with a source ofoxygen in the presence of a catalyst; and further oxidizing methacroleinto methacrylic acid with a source of oxygen in the presence of acatalyst.
 2. The process of claim 1, wherein the mixed oxide catalystused in converting acetic acid to isobutene contains less than 0.14percent by weight of sulfur.
 3. The process of claim 2, wherein thecatalyst contains less than 0.01 percent by weight of sulfur.
 4. Theprocess of claim 3, wherein the catalyst contains less than 0.001percent by weight of sulfur.